This invention relates to a system capable of and a method of displaying on a display device such as a cathode ray tube (CRT) an image of an extended area by processing image data retrieved from an original pictorial image and stored in a memory to reduce their resolution.
One of the methods of displaying data on a display device such as a CRT is to store the image data to be displayed in a memory and to display them on a CRT and the like by sequentially retrieving the stored data from the memory. With a prior art display system which uses this method of display, the area of image data inside the memory which can be simultaneously displayed on the screen is uniquely determined by the number of pixels of the display device such as a CRT. Thus, if it is desired to use such a system to reduce the resolution in order to display image data corresponding to a larger area, a typical routine for such a purpose was to thin the image data in the original memory according to the desired change in resolution, to temporarily store such thinned image data in another memory, and to sequentially retrieve the thinned image data to make a display. A display by such a routine is very time-consuming with a prior art display system, however because new display image data must be preliminarily prepared by first thinning the entire image data in an original memory by a specified ratio. Moreover, there is an additional disadvantage in that an additional memory device of a fairly large capacity is necessary for storing the newly created display image data. For this reason, switching between a normal display operation with the ordinary resolution and a reduced display with lowered resolution cannot be effected quickly and the system itself becomes costly.